Office chairs conventionally provide some type of rearward tilting movement. In its simplest variations, the rear tilting involves solely the back, or the seat and back as a unitary construction. To provide improved and more desirable tilting movement and seating comfort, however, many office-type chairs employ a synchrotilt mechanism coupled between the chair base and the seat-back assembly, for permitting the seat and back to simultaneously tilt at different rates, with the tilt rate and maximum tilt angle of the back typically being about twice the tilt rate and maximum tilt angle of the seat.
Chairs employing synchrotilt mechanisms for permitting simultaneous but relative tilting of the seat and back are well known, and numerous mechanisms have been developed for performing this function. Most of these mechanisms, however, have caused relative motion between the chair and the seated occupant which has interfered with occupant comfort. Such relative motion may involve relative sliding between the seat and the occupant's hips or thighs, and/or sliding between the chair back and the occupant's back, during the relative tilting between the seat and back. In an attempt to alleviate or at least partially compensate for this problem, several chair mechanisms have been developed which cause the seat, during rearward tilting of the seat-back arrangement, to tilt relative to the back about an axis located approximately at the hip axis of the seated occupant. This hip axis is disposed in upwardly spaced relation from the rear portion of the seat, and spaced forwardly from the lower portion of the chair back. While locating the relative tilt axis between the seat and back at the occupant's hip axis is believed to provide improved performance, particularly with respect to minimizing the relative sliding motion between the seated occupant and the seat/back, nevertheless many of these known mechanisms still fail to provide the degree of performance desired, particularly with respect to the desired comfort and ease of movement (often referred to as “ride”) associated with tilting of the chair.
Copending application Ser. No. 09/957,695 filed Sep. 20, 2001, now U.S. Pat. No. 6,644,741, owned by the Assignee hereof, discloses a chair with a synchrotilt mechanism which is believed to provide improved control over the relative but synchronized tilting of the back and seat so as to provide improved occupant comfort and ride while minimizing relative sliding movement between the seated occupant and the back and/or seat of the chair. The synchrotilt mechanism of this chair employs a seat cradle pivotally supported on a back upright, the latter being pivoted from the chair base, and a tilt control linkage cooperatively coupled between the base, seat cradle and upright so that seat tilting occurs generally about an axis disposed above the seat cradle but slightly below an upper surface of the unoccupied seat. The tilt control linkage includes a first lower link pivotally connected at a forward end to the base, a second upper link pivotally connected at a forward end to the seat cradle, and rearward ends of the first and second links pivotally joined to one another and carrying thereon a roller or slide movably captivated within an elongate slot formed within the upright. The forward end of the first link is also pivotally supported within an elongate slot formed in the base, and cooperates with a suitable spring device at this forward end to permit limited forward tilting of the seat cradle relative to the remainder of the chair in response to forward leaning of the chair occupant.
While the aforementioned chair provides desirable performance and seating comfort, nevertheless it has been observed that the synchrotilt mechanism and the tilt control linkage associated therewith require a significant number of parts as well as pivotal connections, which in turn increases the complexity of the chair assembly with respect to required manipulations and assembly time. This linkage also is more space-consuming, particularly in view of the limited available space, and this additionally increases the complexities associated with assembly of the chair.
Accordingly, it is an object of this invention to provide an improved synchrotilt mechanism for a chair which retains the desirable performance, both with respect to control and ride, associated with the chair of Assignee's aforementioned application, but which is able to provide this desirable performance while utilizing a simplified synchrotilt control mechanism which is structurally less complex, occupies less space, is easier to assemble, and is consequently less costly.
More specifically, in the improved chair of this invention, the synchrotilt mechanism employs a seat cradle pivotally supported on the back upright for relative pivoting about an axis typically disposed in the vicinity of the upper surface of the seat, with the relative motion between the seat cradle and back upright being controlled by a tilt control linkage which couples the seat cradle and back upright to the chair base. The tilt control linkage has an elongate control link which at a front end is pivoted to the chair base about a first transverse horizontal axis, which control link at its rearward end has a slide or roller movably engaged within an elongate slot associated with a base leg of the back upright. This control link, where it joins to the back upright, also has a bias or spring arrangement coupled between the seat cradle and the rearward end of the control link to provide a spring-controlled lost motion connection with the seat cradle whereby, during normal rearward tilting of the back upright, the seat cradle also tilts rearwardly but at a lesser rate as permitted by compression of the spring between the control link and the seat cradle. This same spring and the lost motion connection defined thereby also enables the seat cradle to tilt forwardly a limited extent in response to forward leaning of the chair occupant to provide a simple forward tilt function at least when the chair is in the normal upright position.
Other objects and purposes of the invention will be apparent to persons familiar with constructions of this general type upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience in reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. These latter terms will also refer to the normal directions and positional orientations associated with a person sitting in the chair. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the chair and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.